Electrical music system



Feb. 13, 1934. R H, R N ER 1,947,020

ELECTRICAL MUSIC SYSTEM Filed May 29, 1931 5 Sheets-Sheet I M IN VVENTORFeb. 13, 1934. R. H. RANGER 1,947,020

ELECTRICAL MUSIC SYSTEM Filed May 29. 1951 s Sheets-Sheet 2 Feb. 13,1934.

R. H. RANGER ELECTRICAL MUSIC S YSTEM Filed May 29, 1931 S'Sheets-Sheet3 m WWW Feb. 13, R, H. RANGER ELECTRICAL MUSIC SYSTEM Filed May 29, 19515 Sheets-Sheet 4 e as a La 5/ vi INVENTOR 'Feb. 13, 1934. R. H. RANGERELECTRICAL MUSIC SYSTEM s Sheets-Sheet 5 Filed May 29, 1931 QSW JPatented F eb. 13, 1934 UNITED STATES PATENT OFFICE 18 Claims.

My invention relates to a system for producing musical sounds. Asembodiment of such a system, the invention concerns an instrument orapparatus capable of producing musical tones 6 of any desired volume ortimbre throughout the audible range.

Many systems for the production of musical sounds by electricalgeneration, amplification, and reproduction according to the varioustechniques it of the telephonic arts have already been disclosed. Thereare, for example, systems which generate audio frequency oscillations bymeans of a1- ternators, using the physical principle known as Lenzs law.Typical examples of such systems are described in U. S. Letters PatentNos. 580,035; 1,107,261; 1,213,803; 1,213,804; 1,295,691; and 1,749,685.Still other systems utilize a source of high frequency electricaloscillations in combination with a source of variable frequency waves,

causing the well-known heterodyne action and thus producing a beat noteof the desired audible frequency, as disclosed in U. S. Letters PatentNo. 1,661,058 by Mr. L. S. Theremin; and others, as specified in U. S.Letters Patent Nos. 1,376,288

and 1,543,990, use oscillating audion tubes as frequency generators.

All of these systems aim at the production of sustained electricaloscillations or alternating electrical currents of frequencies such thatthey may be apprehended by the human ear when properly translated intocompression and rarefaction waves in a soundconducting medium such asair. The advantages of such electrical generation are manifold; startingwith electrical waves of simple or sinusoidal characteristics, complexwaves may be built up which when rendered audible will produce musicaltones of novel and pleasing quality or timbre; the timbre isconveniently and infinitely variable, allowing one instrument tosimulate many of the classical or fixed timbre type; the amplitude ofseparate tones or combinations of tones is smoothly variable betweenwide limits by simple electrical means; and the pitch and tuning of themusical tones may be made more constant and at the same time far easierto adjust or change than in a non-electrical instrument. These and otheradvantages of electrical musical systems I also have attained in thispresent invention.

My invention differs from all otherelectrical musical systems, however,in that it is not concerned with the generation of pure sinusoidalelectrical waves as a starting point. On the contrary, generators areused which will produce tones of maximum complexity; that is,

tones which contain in addition to simple oscillations of fundamentalfrequency, the greatest possible number of oscillations of harmonlcallyrelated frequencies. These harmonics are then separated from each otherand from their funda- 9 mental tone by electrical or acoustic filteringmeans, their relative amplitudes are adjusted by the performer, and theyare recombined and reproduced. While such a method adds another step-theseparation of complex tones of fllter- 3 ing-to those already necessaryfor an electrical music system, its effect, as will appear below, is toreduce greatly the complexity and cost of the system and to improveits'performance.

' A pure wave, either of sound or of electricity 7 is one whoseprojection to cartesian coordinates with respect to time would appear asthe mathematical figure known as a sine curve; one whose amplitudevaries in simple harmonic fashion. Practically without exception theordinary instruments known to the musical art set up complex sound wavesin the air, and these complex waves have been shown to consist of anumber of pure sound waves'in combination. The principle component purewave is called the fundamental or first partial tone, and sets the pitchof the complex tone. The other components, called harmonics or upperpartials, are generally of less amplitude than the fundamental and ofhigher frequency, than the frequency of the fundamental. The number ofpartials present in a musical tone, as well as their relativefrequencies and amplitudes, determines the characteristic quality ortimbre of the tone, whether string quality, brass quality, siren qualityor the like.

No ordinary musical tone-producer may therefore he used for aninstrumentswhich requires pure tones; it is necessary to resort totuning forks or especially designed alternators, audion circuits, orphotoelectric systems, and elaborate precautions are necessary to insuresteadiness ofpitch and purity of tone in the generated oscillations,while in my invention a simple vibrating body such as a stringor a reedmay be used.

Furthermore, as mentioned above, it is the aim of most electrical musicsystems to produce various synthetic timbre effects by combining puretones in various proportions so as to make available for reproduction avariety of pleasing tone qualities. To accomplish this end they musteither have available pure tones corresponding to the fundamental andthe most important harmonics of each note of the tempered musical scale,or they must employ in place of the proper partials of each complex tonethose tones of the musical scale which most nearly approach the partialsin frequency. In the first case, assuming that a scale of 70 notes isdesired and that six partials are used in each tone, 420 separatesources of pure tones are required, making the instrument; complicated,costly, and difllcult to maintain. In the second case the quality of thecomplex tones produced must of necessity suffer, since the simple tonesused as the upper partials do not bear quite the proper frequencyrelation to each other for such use. In my invention each generator oftone produces both a fundamental tone and all its audible harmonics, sothat only 70 generators are needed to achieve the same result as the 420of the first case cited above.

It is, therefore, a primary object of my invention to develop anelectrical musical system in which there is one tone generator for eachnote of the musical scale, this tone generator providing both thefundamental and all the audible harmonics of that note.

Another object of my invention is to provide an electrical musicalsystem wherein complex tones are separated into their component simpletones so that these may be recombined to give any desired timbre to thesystem.

A further object of my invention is to provide an electrical musicsystem wherein the keying makes or breaks direct current only, thusavoiding the objectionable noises which result when alternating currentcircuits are made or broken.

A fifth object of my invention is to provide an electrical music systemin which some means is provided to prevent any note from being fed tothe amplifying and reproducing system until the operation of keying itsgenerator is over, thus preventing keying noises from becoming audible.

As a sixth object, I wish to provide an electrical music system in whichthe volume of each partial composing a tone is separately controllablein accordance with the timbre of the tone which is to be produced.

The seventh object of my invention is to provide separate amplifiers forparticular groups of tones, both to prevent excessive cross modulationand overloading of the amplifiers, and to insure that tones within acertain frequency range will pass through an amplifier particularlysuited to that range.

The eighth object of my invention is the provision of an electricalmusic system in which tremolo effects involving both frequency andamplitude fluctuations may be introduced into each amplifier to anydesired degree. While either an amplitude variation or a frequencyvariation will give a satisfactory tremolo, a most pleasing effectresults from a combination of the two.

The ninth object of my invention aims to provide a musical systemcapable of simulating the timbre of any one of a number of knowninstruments, the change from one timbre to another being easily andrapidly accomplished.

A tenth object of my invention is to provide means whereby an infiniterange of timbre or tone color is at the command of the performer bymeans of multiple controls permitting the partials of all notes of thescale to be varied simultaneously.

As further objects, my invention aims to provide an electrical musicsystem which may be entirely contained within an ordinary organ console,which is inexpensive to construct and easy to operate and maintain.Still other objects of my invention will become apparent from aconsideration of the following portions of this specification and theappended claims.

To illustrate the principles involved in my invention and its manner ofoperation, I have included as part of my application certain drawings asfollows:

Fig. l, a graphical representation of a typical complex musical tone,and its resolution into simple components; Fig. 2, depicting theconstruction of a single tone generating unit and the keying meansassociated therewith; Fig. 3, which shows a simple reed and an alternatemethod of picking up its vibrations; Fig. 4, a schematic wiring diagramof my musical system for one note of the scale; Fig. 5, a block diagramof my invention for several octaves of the musical scale; Fig. 6, adrawing of the timbre control mechanism for one harmonic; and Fig. 7,showing the application of my invention to a two-manual and pedalconsole.

As the actual generating device for my invention, I have used the reed,long familiar to the musical art as a specially shaped tongue of elasticmaterial, which when fixed at one end in such a manner as to obstruct apassage through which air is being forced under pressure, will vibrateat a definite and constant period depending on the air pressure,producing a musical tone by virtue of the resultant periodicinterruptions of the flow of air. The complex curve C of Fig. 1,represents the wave-form of a typical reed tone, and the sine curves 1to 8 represent the most important pure tones which in combination in thephase and amplitude relations shown make up the complex tone C. in pointof maximum complexity the reed meets most satisfactorily therequirements for tone sources outlined in the objects of my invention.It is also simple and inexpensive in construction,

It is at once apparent that 11'."

and as will appear below, the design technique of the common reed-organor harmonium may easily be applied to a practical embodiment of myinvention.

I do not wish, however, to limit my invention to the use of reeds astone sources; it may well be that considerations of design might make itdesirable to use some other source of complex musical tone such as thestring, the organ pipe, or a sounding plate or membrane, for somespecific embodiment of my invention. It might for instance be desired toadd a musical system of the sort here disclosed to a piano or apipe-organ, instead of to a reed-organ; such an application should bequite possible.

It is not even necessary in fact, that the primary generators for mysystem produce an audible tone, since vibrations of any sort may bepicked up magnetically and fed through the electrical circuits insimilar fashion to the output currents of the microphones in the form ofmy invention described below. Fig. 3, shows how a magnetic pickup may beapplied to a reed. The reed 9, made of some magnetic material such assteel,

is mounted in the conventional manner over the air chamber 10, and isfixed at one end by the screws 11 and 12. As air is forced in eitherdirection through 10, the reed 9 will vibrate in accordance with itscharacteristic tone, periodically varying the reluctance of the path ofthe mag- 1% netic field of the permanent magnet 13. and so inducing inthe field windings 14 an electrical wave corresponding to the normalsound wave of the reed. This electrical wave may then be applied to theinput winding of transformer 15 1 (shown in Fig. 4) in lieu of themicrophone output.

My invention is shown in preferred form for a single note of the scalein Fig. 4. The reed 16 is used as tone generator, and is mechanicallykeyed as in the reed-organ; that is key 17, when depressed by theperformer, causes the dowel pin 18 to open valve 19, admitting air underpressure to the chamber 20. The reed assembly is mounted in asound-insulated box 21, which is connected by the tube 22 to'the soundinsulated mounting 23 of a microphone 24.

The key 17 is so constructed that its first action when being depressedis to open valve 19 and start the reed 16 sounding. Further depressionof the key causes contacts 25 and 26 to close.

- Contact 26 is connected to a source of direct current which fiowsthrough wire 27, the primary winding 28 of transformer 15, and themicrophone 24. The latter thus becomes responsive to the sound wavesreaching it from reed 16 through tube-22, and superposes on theabove-mentioned direct current an alternating electrical wavecorresponding to the complex tone of the reed; i. e., similar to curve Cof Fig. 1.

Up to this point the secondary winding 29 of transformer 15 has beenshort circuited through leads 30 and 31 and the contact points 32 and33. However, mechanical connection has now been established from key 17through the insulating buffer 34 and contacts 25 and 26 to a secondinsulating buffer 35, so that still further depression of the keyseparates contacts 32 and 33, removing the short-circuit fromtransformer winding 29, and allowing the electrical equivalent of thecomplex reed tone to be fed through leads 36 and 37.

At this point it seems pertient to clarify the definition of complextone C. Hereafter, for purposes of simplicity, this term will be takento represent the compound sound wave produced by the reed 16 both in itsaudible and its equivalent electrical forms, as depicted graphically atC in Fig. 1. Similarly, the sinusoidal or pure components of complextone C, shown by curves 1 to 8 of Fig. 1, will be referred to as thefundamental and the first, second, third, fourth, fifth, sixth, andseventh harmonics respectively.

To return now to our consideration of Fig. 4, it has been shown thatfull depression of key 17 by a performer will cause three successiveevents; first, the sounding of reed 16; second, after an intervaldepending on the space between contacts 25 and 26, the energizing ofmicrophone 24, and third, .the removal of the original shortcircuit fromtransformer winding 29. By this arrangement it is ensured that reed 16will have reached a state of steady vibration before its tone is pickedup by microphone 24, and that the amplifying and reproducing circuitswill not become operative until the keying of the microphone isaccomplished, thus preventing any transient phenomena, such as clicks orscratches which might be produced .during the keying operation, frombecoming audible.

After keying is completed, complex tone C.

pedance to alternating currents of any other frequency. For example.assume that reed 18 is tuned to A (A=220 c. p. s. in the tempered scale.The notation of Helmholtz is used throughout this specification tolocate notes of the scale). Filter circuit F1 would then be designed topass all frequencies between 215 and 226 c. p. s., and the firstharmonic of A (=ll-0.0 c. p. s.), the second harmonic of D (=73.42 c. p.s.), the third harmonic of A1 (55.0 c. p. s.), the fourth harmonic of F1(=43.65 c. p. s.) and the fifth harmonic of D1 (=36.71 c. p. s.), aswell as the fundamental tone of reed 16, would pass through the filtercircuitand be impressed on the grid of the UY-227 type vacuum tube 43.On the other hand, the next adjacent fundamental tones of the temperedscale, gt =(207.6 c. p. s.) and at (=233.1 c. p. s.) would be excludedfrom tube 43 by filter circuit F1 as would the harmonics of those toneslower in the scale which are approximately equal to the aliquot parts ofgt and at, and of course all other components of complex tone C outsideof the fundamental.

Thus the fundamental tone of reed 16 passes to tube 43. Afteramplification by this tube it passes through band-pass filter circuit F2consisting of condensers 44, 45, and 46, and inductance 47. Filtercircuit F2, is used to supplement F1 in preventing undesired fundamentaland harmonic tones from passing through the amplifying circuit. Forreasons which will appear below, however, the range of frequencies whichfilter F2 will pass is considerably larger than that of filter F1: isequivalent, in fact, to the frequency range covered by the fundamentalsof nine notes of the tempered scale and such harmonies as approximatethese fundamentals in frequency. Thus, still assuming that thefundamental tone of reed 16 is a, filter F2 would be designed to passall frequencies between 180 and 300 c. p. s., or all fundamental tonesbetween it 115 and d (185.0 and 293.7 0. p. 5.).

Filter circuit F2 must eliminate all undesired components from the tonewhich leaves tube 43, and as we shall see, tube 43 may simultaneously bepassing the amplified output of filter circuit 120 F1 and of five or sixsimilar filter circuits. There is consequently the possibility thatundesirable tones, produced by modulation, may be present in the outputof tube 43, in addition to the harmonies which have not been completelyelimi- 125 nated by the initial filtering. Thus in general it isnecessary that F2 be a more elaborate and efilcient filter than F1. Atwo or three section filter may be required for best results, instead ofthe half-section'type shown.

The filtered output of F2 goes through transformer 48, is amplified bythe power pentode 49, and reproduced by loud-speaker 50, to which itpasses through transformer 51. The amplifying circuits shown in Fig. 4were designed to suit the characteristics of the UY-227 tube 43, and thepentode 49; their operation is well known and requires no extendeddiscussion. Resistors 52 and 53 are of high value and serve to preventlocal oscillations; resistors 54 and 55 are used to hold 14,0 the gridsof tubes 43 and 49 respectively to their 1 proper potentials; condensers56, 57, 58, 59, and are all of two microfarad capacity, and act asby-pass condensers; the choke 61 prevents audio frequency currents fromfeeding back to the B voltage supply; and choke 62 (connected to formwhat is known as a parallel feed circuit) keeps direct current fromreaching the windings of transformer 51. While any good amplifier may beused for my invention, the one shown in Fig. 160

its

4 is peculiarly suited for the purpose, due to its compactness,stability, and high gain.

As we have shown, of the complex tone C emitted by reed l6 and picked upby microphone 24 only the fundamental passes through filter circuit F1to tube 43. Connected to lead 36, however, are a number of additionalresistances exactly similar to 38. These resistances, shown at 63, and64, and in Fig. 4, are each connected through a condenser to a separatefilter circuit similar to F1. Each of these filter circuits is designedto pass a single harmonic of complex tone C; thus the filter connectedto resistor 63 might pass the second harmonic, that connected toresistor 64-the third harmonic, and so on. Resistors are provided for asmany harmonics of the fundamental note as are musically useful, that is,say those of 8000 c. p. 5. frequency or below.

A clearer idea of the operation of my invention may at this point beobtained by a study of Fig. 5, a block diagram of the interrelation ofthe apparatus involved in 27 notes of the tempered scale, from C to d.The tone corresponding to each of these notes is generated by a separatereed, picked up by a separate microphone, and controlled by a separatekey. Thus key Kc controls the action of Rc, which generates the tonecorrespondng to C of the Helmholtz notation, the fundamental pitch being65.41 c. p. s., and also operates microphone Mc, the action of the keybeing as explained for key 1'? of Fig. 4. In similar fashion key K03controls reed Rc z and microphone Mat, and so on up to key Kc,controlling reed Rd and microphone Md. Twenty-seven filter circuits areshown in Fig. 6, lettered Fc, Fat, FD, etc., up to Fe. These filterscorrespond to filter F1, of Fig. 4, and each of them is designed to passa narrow band of frequencies around the fundamental pitch of the note ofthe scale to which it corresponds. Six resistors, lettered I, II, III,IV, V, and VI, respectively, are connected in parallel to the output ofeach microphone, and we shall identify these resistors by the note withwhich they are associated, referring to those of note C as Is, He, IIIc,etc.; to those of note B as In, HE, 1118, etc., and so on. A1, A2, andA3, represent audio amplifiers, AF1, AFz, and AFa, filter amplifiers ofnine-note band width (of filter F2 of Fig. 4), and L1, L2, and La,loud-speakers or other suitable sound reproducers. T1, T2, and T3correspond to the coupling and amplifying tube 43 of Fig. 4.

We will take as example the operation of note C. When key Kc isdepressed by the performer, air is admitted to reed Rc, microphone M0 isenergized. and the short-circuit removed from the secondary of theoutput transformer (not shown) of N10. A complex tone similar to C ofFig. 1 and consisting of a fundamental of 65.41 c. p. s. and numerousharmonics is thus fed to resistors Io, IIc. IIIc. IVc, V0, and VIC. Now,resistor 10 is connected to filter Fc, tuned to pass frequencies between63.50 and 67.40 c. p. s., resistor H0 is connected to filter Fc, whichpasses tones between 127.0 and 134.5 c. p. s., resistor IIIc ties tofilter Fg, passing tones between 190.0 and 213.0 c. p. s., and resistor1V0 is connected to filter Fe, passing a band of frequencies between254.0 and 269.0 0. p. s. The limitations of Fig. 5, do not permit theconnections of resistors V0 and We to be shown. but they are connectedrespectively to filter F0 (passing 320.0 to 330.0 c. p. s.) and Fpassing 380.0 to 403.0 c. p. 5.). Thus, the 65.41

cycle fundamental tone of reed He may pass only through resistor 10,filter Fc, amplifier A1, and filter-amplifier AF1, to be reproduced byloud-speaker Ll. Similarly the 130.8 0. p. s. first harmonic of the noteC finds its only path through resistor IIc, filter Fe, amplifier A2,amplifier filter AF2, and loudspeaker L2, and the 196.23 c. p. 5. secondharmonic of note C goes through IIIc, Fg, A3, AFa, and L3. Thus thecomplex output of reed Rc is separated into its simple components, andeach of these components may be amplified and reproduced separately.

It is now also apparent that each of the simple filters Fc to Fe servesa manifold purposes, passing besides the fundamental tone of itsassociated note the upper harmonics of various other notes. Filter F forexample, is used to separate out the fundamental (:196.0 c.p.s.) of reedR the first harmonic (:1960 c.p.s.) of reed Re, the second harmonic(=196.2 c.p.s.) of reed Re, the third harmonic (:1960 c.p.s.) of reedR01, and the fourth harmonic (=194.5 c.p.s.) of reed Rmt. All of thesetones come within the passband of F; (:190.0 to 213.0 c.p.s.) and so arefed through it. With this method of construction but 72 primary filtersare required in my invention for a scale of 60 notes, as against a totalof 360 primary filters where a separate one is to be provided for eachharmonic of each note.

An essential difference between my invention and other electrical musicsystems lies in the manner in which the ultimate compound tones aresynthetized. Other systems, having produced the simple tones making upthe compound note in the correct proportions for the timbre required,feed them into a single amplifier and reproduce them together. In myinvention, on the other hand, the various components of a note may passthrough different amplifiers and reproducers. We have seen, for instancethat while the fundamental of a note C is reproduced by speaker. L1, thesecond harmonic will emanate from speaker L2, the third and fourthharmonics from L3, and so on. This action'is necessitated by the generaldesign of my system and produces exactly the same musical result as theabove-mentioned method of compounding an entire note in a singlereproducer, since if the numerous reproducers of my system are closetogether and a listener some ten or fifteen feet away, the effect tosuch a listened will be that of a single compound tone made up of allthe tones being simultaneously reproduced. It is of course necessary inmy system that any difference in characteristics between variousamplifier and reproducer groups be compensated for the timbreachustment.

To return for the moment to Fig. 4, the connection of the latter withFig. 5 should now be quite clear. For example, let us say once againthat reed 16 is tuned to a (:220 c.p.s.). Then key 17, reed 16, andmicrophone 24 of Fig. 4 would correspond to key Kg, reed Ru, andmicrophone Ma of Fig. 5. Similarly, resistors 38, 63, 64, and 65 of Fig.4 correspond to resistors Is, 11:1, 111a, and IVs, of Fig. 5. and filterF1 of Fig. 4 is the same as filter Fa of Fig. 5. Coupling tube T3,amplifier A3, amplifier filter AFa, and loudspeaker L3 of Fig. 5 are ofcourse equivalent to tube 43, Filter F2, and loud-speaker c0 of Fig. 4,together with their associated amplifier circuit. Fig. 5 shows that thetone outputs of filters Fit, Fg, F i, Fat, Fe, Fe, Ft' and Fe feed intocoupling tube T3, as well as the output of Fri, and the correspondingpoints of connection of these tones are shown at points 230, 231, 232,233, 234, 235, 236, and 237 in Fig. 4.

The timbre of each note is fixed by the relative values of its sixassociated resistors (see Fig. 5). since each of the latter controls theamplitude of one of the partials or harmonics of the note.

'I have therefore devised a simple, rapid, and

automatic means of setting these resistors so as to produce any one of anumber of predetermined stop qualities. A special gang-control isprovided to vary as a unit all the resistors controlling the same orderof harmonic. In Fig. 5, for instance, one gang-control would regulateresistors Io, lot, In Id, another would control resistors Ho, to IId',etc. Assuming that the regulation of six principal harmonics wereconsidered sufficient to simulate any tone quality, and that myinstrument were built for a -note scale compass, six gang-controls wouldbe necessary, each controlling 60 resistors.

In Fig. 6 I have shown one of these gangcontrols, and have assumed thatit is used to control the amount of second harmonic present in anyreproduced notes. Accordingly, resistors IIIc, IIIcr, IIIp, etc., areshown mounted on shaft 66. These resistors are of the commonrotating-slider type extensively used in broadcast radio receiving sets.They are mounted so that the shaft 66, carrying the sliders 67, 68, 69,etc., rotates freely through their centers. The position of the varioussliders of course determines the values of the various resistors, andthe sliders are so fixed in relation to the shaft and each other thatfor any given position of shaft 66 a given percentage of second harmonicwill be present in every note reproduced by the musical system.

Shaft 66 is driven by a small D. C. shunt motor 70. The shaft passesthrough a fixed pointswitch 101, carrying the ten control pointsnumbered 71 to ,80. Switch blade 102 is mounted on shaft 66, butseparated from it by an insulating bushing 91. Brush 92 makes contactwith blade 102 through bushing 93, and connects it to one end of themotor field 94. Switch points 71 to 80 are connected to mains 81 to 90,and in parallel on these 10 mains are connected the contact fingers of10 relays, only three of which (95, 96,

and 97) are shown in Fig. 6.

Contacts 111 to 120 of relay 95 are connected through leads 81 to tocontact points 71 to w 80 of switch 101, contact 111 connecting throughlead 81 to point 71, contact 112 connecting through lead 82 to point 72,and so on. Similarly, contacts 121 to 130 of relay 96, and contacts 131to 140 of relay 97 are also connected to points 71 to 80.

Let us assume that, with blade 102 on point 74, switch 98 is closed,energizing relay and closing contacts 111 to 120. Through contact 110and contact 231 of a secondary, single-contact relay 230, the coil ofrelay 95 receives just willcient voltage to hold all the relay contactsover, even when switch 98 is opened. Through contacts 111, 112, 113,114, and 115, switch points 71, 72, 73, 74, and 75 receive positivepotential of the proper value for energizing field-coil 94, and

through contacts 116, 117, 118, and 119, switch points 76, 77, 78, and79, receive negative potential of the same value. Motor 70 is soconnected that when positive potential is applied to the free end of itsfield coil it will rotate in a clock wise direction, and conversely,when negative potential is applied, it will rotate in a counterclockwisedirection. Thus, with switch blade 102 on point 74 and the contacts ofrelay 95 closed, motor 70 will start clockwise rotation, carrying withit switch blade 102 as well as the slider arms 67, 68, 69, etc. Blade102 now travels over points 74, 73, 72, and 71, conveying positivepotential from each of them to shunt field 94, until it reaches point80. At this point connection is established between the open end of thecoil of relay 230 and ground, through field-coil 94. Relay 230 issupplied with positive potential of voltage high enough to energize therelay coil, but not high enough to operate motor 70, which consequentlystops. Contact 231 of relay 230 of course opens as soon as the relay isenergized, breaking the holding potential to relay 95 and causing allits associated contacts to open; Resistors IIIc, IIIcii, 1111) etc. havenow been set and the system is again at rest and ready to be readjusted.The secondary relay 230 and its c0ntact2'3l are shown separated fromother portions of the circuit by dotted lines, to avoid confusion withrelay contacts 110 to 119.

Had switch blade 102 been on one of the nega-v tive points 76, 77, 78,or 79, rotation of the motor would have been counter-clockwise, againuntil neutral point 80 was reached.

If the action of relays 96 and 97 is followed through, it will be foundexactly similar to that of relay 96, except that the neutral point uponwhich the blade 102 comes to rest is different in each case. Thus whenswitch 99 is closed, energizing relay 96, blade 102 is brought aroundfrom any position it may be in to point 79, and when switch 100 isclosed relay 97 causes the motor to operate until blade 102 rests onpoint 78. In similar fashion, closing the switch of any one of the tenrelays contained in the complete gangcontrol will rotate shaft 66 untilblade 102 rests on the point corresponding to that relayin other words,ten different second-harmonic signal levels are at the command of theperformer.

A complete quality-setting control for the entire system would of courseinvolve a means of setting all harmonics contained in the notesreproduced by the sys'tem. This would be most simply achieved byproviding six-pole singlethrow push button switches for each stop". Eachpole of a stop switch will act as the starting switch (for example,switch 98 of Fig. 6) for that relay of the gang-control on each harmonicwhich gives the desired signal-level for that harmonic. 5

These buttons will be pushed momentarily and then released, just as arethe combination-setting buttons on a modern-pipe-organ, and a signallight may be provided for each, to indicate the button last operated.Since in the embodiment we have described six harmonics are used, eachhaving ten possible settings, it is apparent that 1,000,000 stops may beprovided, each producing a different timbre. Of course, no practicalinstrument either requires or can make use of more than a few hundredstops, and for this reason it will generally be necessary to have nomore than three or four settings of any of the gang-control resistorsavailable.

For an inexpensive and yet most flexiblemusical instrument, the physicalform of my invention may be made similar to that of the well-knownreed-organ or harmonium. Fig. 2 shows how a key, reed, and microphonemight be mounted in such an instrument. Pressure on key 141, transmittedthrough the dowel stick 142, opens valve 143, and admits air to reed144, exactly as in the 145 leads the complex sound wave to microphone146, which is flexibly suspended as shown from some point of support 147so as to minimize vibratory and resonance effects. Tube 145 should be asshort as is consistent with a practicable arrangement of themicrophones, since otherwise there will be too great a decrement in theintensity of the sound waves over its length, and for the same reason itshould be made of some fairly resilient material such as brass. Bydeepening by a few inches the space ordinarily used to mount the reedsin a harmonium, it may be used to contain the microphones and microphonetransformers as well as the reeds. The timbre-regulating gang-controlresistors may be mounted to'the rear of the console at the same level asthe microphones; the primary filters may be installed on the next levelbelow, and the amplifier filters, amplifiers, and loud speakers at thebottom. The rear cover of the console forms an ideal sounding board forthe reproducers.

The actual finger-pressure required of the performer to operate thevalve-mechanism of a reed is normally rather high, as compared to theaction of a modern pianoforte or electrically keyed pipeorgan. Since theplaying of a key in my invention must not only operate the reed but mustin addition close numerous spring contacts, it is desirable, in order tofacilitate rapid passage work, to provide a measure of mechanicalassistance for the keying operation.

The construction of my approved means to this end is shown in Fig. 2,wherein 148 and 149 represent cross-sectional areas through a solenoidsurrounding the lower end of dowel 142, the shaded section 150 of whichis of magnetic material such as iron. The light spring 151 normallybears against pin 152, holding key 141 slightly away from dowel 142. Italso forms part of a contact device of which point 153 is the otherportion. This contact closes when key 141 is pressed, energizingsolenoid 148149, which by attracting magnetic piece 150 assists inkeying the reed 144. As soon as pressure is removed from key 141, springcontact 151 will disconnect the solenoid and permit the heavier spring154 to restore the valve, dowel and key to their original positions.

Air under pressure may of course be supplied to the reeds in a number ofdifferent ways. Perhaps the most satisfactory method is to use a smallsilent electric blower unit of the type extensively employed forelectric pianos. The insertion of a small electrically operated "shakerbellows in the air line, controlled by a switch or stop, will provide amost satisfactory tremolo. An intensity-varying tremolo such asdescribed in my application, Serial No. 417,466, filed Dec. 30, 1929,now Patent No. 1,901,985, dated March 21, 1933, may be used tosupplement the air tremolo if desired.

Two types of volume control may be applied to my invention. As anoverall control, varying the volume of the entire range of theinstrument as a unit, a suitable pedal-operated variable resistance maybe inserted in series with the D. C. power supply to the microphone, asis resistance 155 in Fig. 4. As power is supplied to all the microphonesfrom a single source, setting this single resistance will suffice tovary the output signal level of the instrument. In addition to in Fig.4.)

by separate control levers or pedals, may be used at the discretion ofthe performer to vary the relative loudness of groups of tones ofvarious pitches; accentuating, for example, the bass orthe solo part ofa composition.

While the instrument described in the above three paragraphs wouldprobably be the most suitable form of my invention for use in the home,it might be that for other purposes, such as concert-hall or theatreuse, a more elaborate instrument would be needed. Accordingly, I haveshown in Fig. 7 how with a quite inconsiderable increase in complexitymy invention may be embodied in an instrument having a fiexibility andpower rangeequal to the largest, pipeorgans.

We will assume for simplicity that our instrument is to be controlled bytwo manuals and a pedal keyboard. Keys 157, 158, and 159 each operate areed tuned to produce note C (65.41 c. p. s.), 157 being one of thechoir manual keys, 158 one of the swell manual keys and 159 one of thepedal keys. Under each of these keys are mounted eight contacts,operating on a set schedule according to their height as shown in Fig.7; i. e., were key 157 to be depressed, it would first admit air to reed168 and then close contact 160, energizing the circuit of microphone169. Following this, contacts 161, to 166 would close simultaneously,and lastly, contact 167 would open, removing the short-circuit from thesecondary winding of microphone transformer 170.

The tone outputs of microphones 169, 179, and 189, passing throughtransformer 170, 180, and 190 go to the resistor groups 201 to 206, 211to 216, and 221 to 226. Up to this point the operation of the three keyshas been identical and similar to that of key 17 of Fig. 4, but now thetones, instead of feeding directly from the timbre resistors to theprimary filter circuits, feed back to the six simultaneously closingcontacts under each key, and are thence distributed to the appropriatefilters Fe, Fe, F Fe, Fe, and Fg'. Thus the fundamental of the complextone produced by reed 168 passes through filter Fe, reaching it throughresistor 201 and contact 161. Similarly, the first harmonic of the samecomplex tone passes through Fc, by way of resistor 202 and contact 162,the second harmonic reaches Fg, through resistor 203 and contact 163,etc. In exactly the same manner, filter F0 handles the fundamental ofthe complex tone produced by reed 188 when key 159' is operated; Feseparates out the first harmonic of the complex tone produced by reed178 when the closing of key 158 passes tone to it through resistor 212,and contact 172, and the first harmonic of the complex tone produced byreed 188 when permitted to do so by the closure of contact 182; andfilter F performs a like function for the second harmonies of thecomplex tones produced by reeds 178 and 188.

By the design shown in Fig. 7, then, I am able to use the same set ofprimary filters for a multi- Since the timbre resistors is prevented,and since the amplifiers are not operative before the short-circuits arere moved from the microphone transformers, there is no danger of keyingnoises becoming audible.

For each manual of the larger instrument I thus provide a separate setof reeds, microphones,

-oil

microphone transformers, and gang-control resistors. Only one set ofprimary filters, filterampliflers, and loud-speakers is necessary forthe entire'installation. If the instrument is to from the console: theirexact location should be determined for maximum efficiency under theacoustic conditions prevailing in the hall. Two

or more consoles may of course be used if desirable.

I'do not wish to limit my invention to any of the above describedpatterns. since many different forms of instrument employing the sameprinciples will readily suggest themselves to those skilled in themusical and electrical arts. I therefore believe myself entitled to makeand use any and all of such modifications as fall fairly'within thespirit and scope of my invention as' defined by the appended claims. 7 I

What I claim and desire to secure by Letters 7 Patent is the following:

1. In an electrical music system, a plurality of generators of complextones equal in number to the notes of the system. a plurality oftone-filtering devices each capable of segregating the fundamental toneof. a] single one or said generators, as

well as those upper partial tones of other generators which approachsaldfundamental tone more closely in frequency than .they do any otherfundamental tone, from all other tones of the system, and means forreproducing simultaneously the tones passed by said tonedllteringdevices.

2. In an electrical music system. a plurality of generators ofcomplex'tones equal in number to the notes of the system, a plurality oftone-filtering'devices associated therewith for the purpose ofseparating said complex tones into their simple component tones,amplifying systems of a number 'lessthan the number of notes in thesystem, a secondary tone-filtering device, and a sound reproducel'connected'with each of said amplifying systems.

3. In an electrical music system, a plurality of generators of complextones equal in number to the notes of the system, a plurality of primarytone-filtering devices equal in number to the notes of the system plusthose additional notes found by following the musical scale of thesystem above the highest pitched generated complex tone of the system tothe audible limit, the frequency pass-band of each of said primarytone-filtering devices including the fundamental tone of a single one ofsaid generators as well as those upper partial tones of others of saidgenerators which approach said fundamental tone more closely infrequency than they do the fundamental tone of any other complex tone ofthe system, secondary toneflltering devices of a number less than thenumber of .notes in the system but greater than the number of musicaloctaves in the system, the frequency pass-band of each of said secondarytone-filtering devices including the fundamental tones of a group ofadjacent notes covering a range of less than one octave, and means foramplifying and reproducing the outputs of said secondary tone-fil- 4tering devices.

a said body to vibrate, means for translating the vibrations, of saidbody into electrical waves,"

' 4. A system for the production of musical tones comprising a resonantbody, means for causing means for. amplifying said electricalwaves,means for translating said amplifiedv electrical waves into audibletones, and means for delaying the admission of said electrical waves tosaid amplifying means until such time as said vibrating body shall havereached a steady state of vibration.

5.,In an electrical music system, a plurality of sources of complextones, means for separating said complex tones into their various simplecomponent tones, means for amplifying said component tones, means forreproducing said complex tones simultaneously, and means for de-' layingthe admission of the output of said sources of complex tones to there'stof the system until suchtime as said sources shall have reached asteady operating state.

6. In an electrical music system, a generator of audible complex tone,means for translating said audible complex tone into a complexelectrical wave, means for separating said complex electrical wave intoits component pure electrical waves. means for separately varying theamplitude of each of. said pure electrical waves, andmeans for renderingsaid pure electrical waves simultaneously audible. I

7.. In an electrical music system, a plurality of generators of audiblecomplex tones corresponding in number to'the notes of the-system- ,-acorresponding number of microphones, each picking up the tone of oneofsaid generators and trans lating it into a complex'electrical wave, apinrality of electrical wave filters equalin number to the notes of thesystem plus those additional notes found by following the musical scaleof the system above the highest pitched generated complex tone of thesystem to the audible limit, the frequency pass-band of each of saidfilters including the fundamental tone of a single one of saidgenerators as well as those upper partial tones of others of said,generators which approach said fundamental tone more closely infrequency than they do the fundamental tone of any other complex tone ofthe system, keying means causing the said generators to becomeoperative,

the microphones to become receptive tothe outputs of said generators,and the outputs of said microphones to pass to said electrical wavefilters, these operations occurring in the order named and variousgenerators being keyed according to the will of the performer, and meansfor controlling the relative amplitudes and simultaneously reproducingthe outputs of said electrical wave filters. v

8. In combination in an electrical music system, a plurality of reeds, acorresponding plurality of microphones associated with said reeds, aplurality of primary electrical wave filters for the purpose ofseparating the complex tone outputs of said microphones into componentpure waves, a r

plurality of resistors so arranged as to vary in similar fashion therelative amplitudes of the component pure waves making up each of said Icomplex tone microphone outputs, a plurality of secondary electricalwave filters each purifying a microphone associated with said reed, asource of operating potential for said microphone, means for amplifyingand reproducing audibly the output of said microphone, a manuallyoperated key, and means operable from said key for opening said airvalve, for applying said operating potential to said microphone, and forconnecting the said output of the said microphone to the said amplifierand reproducing means, in the order named.

10. An electrical music system comprising a reed, a source of air underpressure for the purpose of vibrating said reed, an air valvecontrolling the flow of air from said source to said reed, a microphoneassociated with said reed, a source of operating potential for saidmicrophone, a plurality of primary electrical wave-filtersfor thepurpose of separating the complex tone output of said microphone intoits component pure waves, means for varying the relative amplitude ofeach of said pure waves, a secondary wave-filter for purifying theoutput of each of said primary wave-filters, means for amplifying andreproducing audibly the outputs of said secondary wavefilters, amanually operated key, and means operable from said key for opening saidair valve, for applying said operating potential to said microphone, andfor connecting the said output of the said microphone to the saidprimary electrical wave-filters, in the order named.

11. In an electrical music system as described in claim 9, a means ofcontrol for the overall volume of the system comprising a variableresistance in series with the operating potential supplied to themicrophone oi the system.

12. A tremolo control for an electrical music system as described inclaim 9 comprising a motor, means for controlling said motor, and meansoperable from said motor for causing a periodic variation in thepressure of the air applied to the reed in said electrical music system.

13. A tremolo control for an electrical music system as described inclaim 9 comprising a motor, means for controlling said motor, and ashaker bellows in the air line between the source of air under pressureand the reed in said electrical music system, said bellows beingoperable from said motor.

14. A timbre-setting device for an electrical music system as describedin claim 8 comprising a motor, means for controlling said motor, and

means operable from said motor for causing a change in the setting ofthose resistors controlling the amplitudes of the component tones of agiven harmonic order of every complex note produced by the system.

15. A timbre-setting device for an electrical music system as describedin claim 7 comprising a plurality of variable electrical resistorscontrolling the amplitude of a given order of partial of each of thecomplex tones produced by the system and mounted on a shaft in suchfashion that rotation of the said shaft will cause a uniform change insetting in all the said resistors, a motor rotating said shaft, andmeans for controlling the said motor.

16. In an electrical music system comprising a plurality of soundingreeds, a plurality of microphones associated with said reeds, electricalwave filters separating the outputs of said microphones into simpletones, and means for amplifying and reproducing the outputs of said wavefilters, a keying system including means for electrically dissociatingsaid microphonesfrom said wave filters except when said reeds aresounded.

17. The method of operating an electrical music system which includesthe production of compound sound waves, the translation of said soundwaves into compound electrical waves, the separation of said complexelectrical waves into their component pure electrical waves, theseparate amplification or reduction of each of said simple waves, andthe coordination of said simple waves with a suitable amplifying andreproducing system.

18. A system for the production of musical tones comprising a reed,means for causing said reed to sound, means for producing electricalwaves in accordance with the sound waves produced by said reed, meansfor separating the harmonic components of said electrical waves, meansfor amplifying or reducing separately each of said harmonic components,and means for translating said harmonic components simultaneously intoaudible tones.

RICHARD nownmn RANGER.

